The present invention relates generally to catheters systems. In particular, the present invention is directed to a catheter system that provides for the controlled longitudinal movement of an elongate element--such as a rotatable imaging core with an ultrasonic transducer or an optical fiber imaging device at its distal end, or a drive cable with an atherectomy cutter at its distal end-housed within a sheath positioned within a patient.
Arteriosclerosis, also known as atherosclerosis, is a common human ailment arising from the deposition of fatty-like substances, referred to as atheromas or plaque, on the walls of blood vessels. Such deposits occur in both peripheral blood vessels which feed the limbs of the body and the coronary vessels which feed the heart. When the deposits accumulate in localized regions of a blood vessel, stenosis, or narrowing of the vascular channel, occurs. Blood flow is restricted and the person's health is at serious risk.
Numerous approaches for reducing and removing such vascular deposits have been proposed, including balloon angioplasty where a balloon-tipped catheter is used to dilate a region of atheroma, and other devices that are pushed or pulled along or through a deposit, such as atherectomy where a blade or cutting bit is used to sever and remove the atheroma, spark gap reduction in which an electrical spark burns through the plaque, laser angioplasty where laser energy is used to ablate at least a portion of the atheroma, and opening of vessels through the use of stents.
Two major difficulties in using such devices are maintaining a constant translational rate for the device and obtaining images of and information on the region of the blood vessel to be treated. Several imaging techniques have been proposed. Catheters incorporating mechanical rotation of ultrasonic transducers for imaging are disclosed in U.S. Pat. Nos. 4,794,931; 5,000,185; 5,049,130; and 5,024,234. These catheters scan in a plane normal to the catheter axis. Catheters employing phased array imaging systems are disclosed in U.S. Pat. Nos. 4,841,977 and 4,917,097. Catheters employing fiber optic imaging components are also known.
Generally deposits extend some longitudinal distance along the length of a vessel. To view different portions of the deposit a physician typically moves a handle attached to a proximal end of the imaging catheter along the vessel, for example, by pushing or pulling the catheter.
Imaging using computer-assisted reconstruction algorithms enables physicians to view a representation of the patient's interior intravascular structures in two or three dimensions (i.e., so-called three-dimensional or longitudinal view reconstruction). In this connection, image reconstruction algorithms typically employ data-averaging techniques which assume that the intravascular structure between an adjacent pair of data samples will simply be an average of each such data sample. Thus, the algorithms use graphical "fill in" techniques to depict a selected section of a patient's vascular system under investigation. Of course, if data samples are not sufficiently closely spaced, then lesions and/or other vessel abnormalities may in fact remain undetected (i.e., since they might lie between a pair of data samples and thereby be "masked" by the image reconstruction algorithms mentioned previously).
Even with the most skilled physician, it is practically impossible to manually exercise sufficiently slow constant rate longitudinal translation of the ultrasound imaging device (which thereby provides for a precisely known separation distance between adjacent data samples). In addition, with manual translation, the physician must manipulate the translation device while observing the conventional two-dimensional sectional images. This division of the physician's attention and difficulty in providing a sufficiently slow constant translation rate can result in some diagnostic information being missed. To minimize the risk that diagnostic information is missed, it is necessary to lengthen the imaging scan time which may be stressful to the patient. Similarly, it is difficult for physicians to manually control the translational rate of atherectomy catheters and other interventional devices that are longitudinally advanced and retracted through blood vessel and other body lumens.
U.S. Pat. No. 5,485,486 discloses an ultrasound imaging transducer which is capable of being translated longitudinally within a section of a patient's vascular system at a precise constant rate through the use of a longitudinal translation assembly. The longitudinal translation assembly moves the entire rotary drive assembly to provide the desired longitudinal movement of the transducer. Such an ability enables a series of precisely separated data samples to be obtained thereby minimizing (if not eliminating) distorted and/or inaccurate reconstructions of the ultrasonically scanned vessel section (i.e., since a greater number of more closely spaced data samples can reliably be obtained). Also, such an assembly can be operated in a "hands-off" manner which allows the physician to devote his or her attention entirely to the real-time images with the assurance that all sections of the vessel are displayed. While such a longitudinal translation assembly can work well, it is relatively large, bulky and heavy; it is expensive; and it is cumbersome to set up, in part because the rotary drive and longitudinal translation assemblies are wrapped in separate sterile drapes (plastic bags) for sterility.
One drawback with conventional catheter imaging systems is the cost of replacing the disposable catheter assembly. The catheter assembly is mounted to a draped pullback assembly for use, used and then discarded after use. However, the catheter assembly includes the electronics necessary to send, receive and filter signals. These electronic components are disposed of with the rest of the catheter assembly which raises the cost of the procedure.